In Stephen Y. Chou and Wenyong Deng, "Subwavelength Amorphous silicon transmission gratings and applications in polarizers and waveplates", Appl. Phys. Lett., 67 (6), pp.742-744, Aug. 7, 1995 there is described a fabrication and an experimental evaluation of subwavelength gratings consisting of a patterned layer amorphous silicon on a planar silica substrate. Measurements on this structure show (for normal incidence) a very different behaviour between TE and TM operation, and for one particular parameter set, transmission for the TM-mode is very low. Detailed calculations on this structure, according to the "Rigourous Coupled Wave Analysis" method show that for this particular configuration the specular TM reflection is as high as 91.6%.
It is to be noted that the period of the gratings is smaller than the wavelength in the substrate and superstrate and that this structure is to be illuminated from the low refractive index side.
In Henry L. Bertoni, Li-Hsiang S. Cheo, and Theodor Tamir, "Frequency-Selective Reflection and Transmission by a Periodic Dielectric Layer", IEEE Transactions on Antennas and Propagation, Vol. 37, no.1, pp. 78-86, January 1989, there is described a dielectric structure exhibiting a complex behaviour in terms of reflection/transmission characteristics as a function of frequency, offering close to 100% reflection for properly chosen parameters.
The principle of operation relies on exciting a guided mode in a grating layer, propagating along the direction parallel to the layer direction. This waveguide mode is actually a leaky mode, due to the periodic nature of the waveguide. For properly chosen parameters, this excited mode couples for nearly 100% to zero order in reflection or transmission.
This implies that only structures with a high refractive index grating layer between a relatively low index substrate and superstrate are suitable. Furthermore this principle only works for oblique incidence.
U.S. Pat. No. 5,255,278 relates to semiconductor laser comprising a mirror having a dielectric layer with a grating structure etched in the dielectric layer whereon the metal layer is deposited. A high reflectivity is obtained by using the covering metal layer. This mirror is appropriate only for substrate-side emitting lasers.